Polarization-enhanced photovoltaic response and mechanisms in Ni-doped (Bi0.93Gd0.07)FeO3 ceramics for self-powered photodetector

Multiferroic toxicity-free perovskite BiFeO₃-based materials reveal potentials in photoelectrical conversion, energy harvesting and photodetector. This work highlights polarization-enhanced photovoltaic (PV) effects and mechanisms in B-site Ni-doped (Bi_0.93Gd_0.07)FeO₃ ceramics with indium tin oxide (top electrode) and Au (bottom electrode) thin films. The enhanced PV effects are attributed to the reduced bandgap, polarization-modulated Schottky barrier, increased O 2p-Fe 3d orbital hybridization, and nucleation of domain walls to improve transportation of charge carriers. Improved PV parameters of responsivity (R) ～1.71 × 10^?2 A/W, detectivity (D*) ～9.56 × 10¹¹ Hz^1/2/W (Jones), open-circuit voltage (V_oc) ～0.65 V, and short-circuit current density (J_sc) ～80 μA/cm² were obtained from the ITO/ (Bi_0.93Gd_0.07)(Fe_0.97Ni_0.03)O₃/ Au heterostructure after 2 kV/cm poling under 405 nm irradiation at 10³ W/m² intensity. This work demonstrates that Ni-doped (Bi_0.93Gd_0.07)FeO₃ ceramics can be potential candidates for self-powered UV photodetector.     

Improving the fabrication uniformity of ZnO nanowire UV sensor by step-corner growth mode

Uniformity in mass-fabrication of nanostructured device is important for its practical application. In this paper, we developed a step-corner growth mode to on-chip fabricate uniform oblique-bridged ZnO nanowire UV sensor. By strictly controlling the microelectronic processing including photolithography and magnetron sputtering procedures during the seed layer deposition and electrode fabrication, ZnO NW array could nucleate at the upper step-corner of the seed layer due to the high catalytic activities at the surface steps and kinks, and then grow in a distribution of circular sector to form an oblique bridging configuration, which guaranteed the device performance and uniformity at the same time. For the within-chip uniformity, in a 4?×?4 sensor array that randomly chosen under the 365?nm UV light of 2.5?mW/cm² and at the bias voltage of 1?V, the light-to-dark current ratio all kept in the level of 10⁶ with the average value of 1.84?×?10⁶. There were 75% of them in the range of 1.1?×?10⁶ ~ 3?×?10⁶. The detectivity all kept in the level of 10¹⁵Jones with the average value of 3.53?×?10¹⁵Jones. There were 75% of them in the range of 2?×?10¹⁵ ~4?×?10¹⁵Jones. For the chip-to-chip uniformity, in 12 packaged devices that randomly chosen from three fabrication lots, the light-to-dark current ratio all kept in the level of 10⁶ with the average value of 2.70?×?10⁶. There were 75% of them in the range of 1?×?10⁶~ 3?×?10⁶. The detectivity all kept in the level of 10¹⁵Jones with average value of 3.69?×?10¹⁵Jones. There were 75% of them in the range of 1?×?10¹⁵ ~ 4?×?10¹⁵Jones. The uniformity would deteriorate if the step height of seed layer was short, because NW would nucleate at the lower corner of the step and difficult to form the oblique bridge. Fabrication uniformity was also influenced by the step exposure degree, the compactness of the seed layer and the flatness of the substrate.     

Self-powered high-performance topological crystalline insulators tin selenide/silicon dioxide/silicon heterojunction broadband photodetectors for weak signal detection

Topological crystalline insulators have been demonstrated to possess a broadband absorption spectrum owing to the gapless topological surface states and narrow bulk band gap, which are promising candidates for new generation optoelectronic devices application. Herein, we fabricated a high-quality topological crystalline insulator tin selenide (SnSe)/SiO₂/Si heterostructure using a simple magnetron sputtering method. Our strategy is to build high-quality heterojunctions on silicon wafers by directly growing films to achieve sufficiently large interfacial barriers, enhance the photovoltaic effect of heterojunctions, and make heterojunctions achieve better photo response characteristics. At zero voltage, the current of heterojunction varies from extremely low dark current (∼10⁻¹⁰ A) to high photocurrent (∼10⁻⁵ A). These advantages make the SnSe/SiO₂/Si heterostructure show a superior photoresponsivity of 39.2 AW⁻¹, an excellent detectivity (D*) of 4.2 × 10¹⁶ cmHz^1/2W⁻¹, a large broadband photoresponse from 365 nm–980 nm and a fast response speed of approximately microseconds. The over-all properties have greatly exceeded those of the reported 2D-based vertical VDW heterojunctions, those 2D film/Si heterojunctions and other Topological insulators/Si heterojunctions photodetectors respecting D*, on-off ratio, bandwidth etc. The SnSe/SiO₂/Si heterojunctions will provide more chance for future optoelectronic devices applications.     

Self-powered broadband α-MoO3/Si photodetector based on photo-induced thermoelectric effect

As a two-dimensional crystal, molybdenum trioxides (α-MoO₃) has been considered as a typical candidate for next-generation photodetectors (PDs) but with limited photodetection applications in the ultraviolet region. Here, a photo-induced thermoelectric (PTE) effect in α-MoO₃ is proposed as a practical approach to realize the broadband photodetection of α-MoO₃/Si heterojunction PDs. High-quality α-MoO₃ films are grown on Si by using an e-beam evaporation method. By modulating the photo-induced thermoelectric potential along the c-axis on the transport properties, the α-MoO₃/Si PDs can be operated as a self-powered device, showing broadband photoresponse beyond the bandgap limitation in the wavelength range of 405–1550 nm. The manipulation of the PTE effect in the heterojunction is investigated carefully, clarifying the corresponding physical mechanisms of the unique photoresponse behaviors. Furthermore, the fabricated device exhibits competitive photodetection performance with a high photoresponsivity of 63.3 mA/W, a high optical detectivity of 3.1 × 10¹¹ cm Hz^1/2W^?1, fast response speeds with the rise/fall times of 0.47/0.76 ms, as well as high durability and environmental stability under 980-nm infrared illumination. These results not only provide a novel strategy to develop novel PDs with high performance, but also supply a deeply understanding of the PTE effect in α-MoO₃/Si heterojunctions.     

Broadband,high-sensitivity self-powered ferroelectric LuMnO3-based photodetector with large photocurrent output

The broadband spectrum detection from ultraviolet to near-infrared is hankered in the photoelectric applications of imaging, sensing and communication. Here, a new self-powered photodetector based on ferroelectric LuMnO₃ thin film with a narrow bandgap of 1.46 eV exhibits high-sensitivity ultraviolet–visible–near infrared photodetection properties. The responsivity (R) and detectivity (D*) in sunlight are 0.4 A/W and 7.05 × 10¹¹ Jones, which are much higher than that of other ferroelectric photodetectors. Moreover, under the monochromatic light (900 nm), the R and D* can reach 0.39 A/W and 6.89 × 10¹¹ Jones. The outstanding photodetection performances owed to the large photocurrent output, where the short-circuit current density can reach 10.5 mA/cm² under 1 sun illumination. The synergistic effect of ferroelectric photovoltaic effect and interface barrier effect demonstrates that the multi-driving forces can achieve high dissociation efficiency for photon-generated carriers. The excellent photodetection performances open up new application of ferroelectric materials in broadband self-powered photodetectors.     

In-situ prepared WSe2/Si 2D-3D vertical heterojunction for high performance self-driven photodetector

Two-dimensional (2D) transition metal chalcogenides (TMDs) have shown tremendous feasibility as building blocks for the development of high-performance optoelectronic devices owing to their distinct electrical and optical properties. However, the relatively narrow sensing range as well as the complex fabrication technique impede their technological applications. Here, we demonstrate the mixed-dimensional van der Waals (vdW) WSe₂/Si 2D-3D vertical heterojunction by in-situ fabrication of WSe₂ multilayer on pre-patterned Si, for broadband and fast-speed photodetection. Thanks to the novel high-quality vertical p-n heterojunction, the as-fabricated WSe₂/Si photodetector shows an excellent rectifying characteristic and a prominent photovoltaic effect, making the device capable of light detection in self-driven mode. Additionally, the device reveals remarkable performance in terms of a high specific detectivity of ～8.79 × 10¹³ Jones, a large responsivity of ～294 mA/W, and a fast response time of 4.1 μs. Significantly, the device shows high sensitivity to a wide spectra (200–1550 nm) owing to the production of a type-II band structure of the WSe₂/Si vertical heterojunction. The mechanism of photo-generated carriers separation and transfer in the heterojunction is analyzed by KPFM. Our work offers a potential route to the development of unique 2D-3D heterojunction for optoelectronic devices and system applications.     

Improved stability in P3HT:PCBM photovoltaics by incorporation of well‐designed polythiophene/graphene compositions

Morphological and photovoltaic stabilities of poly(3‐hexylthiophene) (P3HT):phenyl‐C₆₁‐butyric acid methyl ester (PC₇₁BM) solar cells were investigated in pristine and modified states. To this end, four types of patterned/assembled nanostructures, namely reduced graphene oxide (rGO)‐g‐poly(3‐dodecylthiophene)/P3HT patched‐like pattern, rGO–polythiophene/P3HT/PC₇₁BM nanofiber, rGO‐g‐P3HT/P3HT cake‐like pattern and supra(polyaniline (PANI)‐g‐rGO/P3HT), were designed on the basis of rGO and various conjugated polymers. Intermediately covered rGO nanosheets by P3HT crystals (supra(PANI‐g‐rGO/P3HT)) performed better than sparsely (patched‐like pattern) and fully (cake‐like pattern) covered ones in P3HT:PC₇₁BM solar cell systems. Supra(PANI‐g‐rGO/P3HT) nanohybrids largely phase‐separated in active layers (root mean square = 0.88 nm) and also led to the highest performance (power conversion efficiency of 5.74%). The photovoltaic characteristics demonstrated decreasing trends during air aging for all devices, but with distinct slopes. The steepest decreasing plots were obtained for the unmodified P3HT:PC₇₁BM devices (from 1.77% to 0.28%). The two supramolecules with the most ordered structures, that is, cake‐like pattern (10.12 mA cm^?2, 51%, 0.58 V, 2.2 × 10^?6 cm² V^?1 s^?1, 4.3 × 10^?5 cm² V^?1 s^?1, 0.69 nm and 2.99%) and supra(PANI‐g‐rGO/P3HT) (12.51 mA cm^?2, 57%, 0.63 V, 1.2 × 10^?5 cm² V^?1 s^?1, 3.4 × 10^?4 cm² V^?1 s^?1, 0.82 nm and 4.49%), strongly retained morphological and photovoltaic stabilities in P3HT:PC₇₁BM devices after 1 month of air aging. According to the morphological, optical, photovoltaic and electrochemical results, the supra(PANI‐g‐rGO/P3HT) nanohybrid was the best candidate for stabilizing P3HT:PC₇₁BM solar cells. © 2020 Society of Chemical Industry     

Self-driven heterostructure photodetector of sputtered CZTS film on c-Si with an inverted pyramid structure

Ag has been incorporated into the CZTS film through post-doping by magnetron sputtering to decrease the Cu_Zn anti-site defect. Efforts have been dedicated to optimize the Ag sputtering time and 60 s will be the best as surveyed from the SEM, XRD and Raman spectra. Then the broad-band self-driven heterostructure photodetector has been manufactured by combining the CZTS and inverted pyramid n-Si (IP n-Si). The device represents the first-rank property under the irradiation of 5 mW, 780 nm LED with 0 V bias with the responsivity and detectivity of 7.2 mA/W and 4.98 × 10¹⁰ Jones respectively. The device can persist excellent linearity when enduring a 40 mW-80 mW, 980 nm NIR laser with 0 V bias. The comprehensive performance becomes the best under the irradiation of a 50 mW laser. The responsivity and detectivity are 1.22 mA/W and 1.98 × 10¹⁰ Jones. The device can also work stably as the laser changes from 1 Hz to 15 kHz. The rise time and decay time are 93.3 μs and 141.0 μs respectively. These results open up an innovative application for CZTS to build a broad-band self-driven photodetector as a window-layer.     

Effects of Tb doping on structural and electrical properties of 47(Ba0.7Ca0.3)TiO3–0.53Ba(Zr0.2Ti0.8)O3 thin films at various annealing temperature by pulsed laser deposition

The ceramic thin films of 47(Ba_0.7Ca_0.3)TiO₃–0.53Ba(Zr_0.2Ti_0.8)O₃ (BCZT) + x (x = 0.2, 0.3, 0.4 and 0.5) mol% Tb were grown on Pt(111)/Si substrates with various annealing temperature by pulsed laser deposition. The XRD spectra confirm that Tb element can enhance the (l10) and (111) orientations in ceramic films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that Tb-doping can increase particle size effectively. The surface of Tb-doped film annealed at 800 ℃ is uniform and crack-free, and the average particle size and mean square roughness (RMS) are about 280 nm and 4.4 nm, respectively. Comparing with pure BCZT, the residual polarization (P_r) of 0.4 mol% Tb-doped film annealed at 800 ℃ increase from 3.6 to 9.8 μC/cm². Moreover, the leakage current density value of Tb doped films are one order of magnitude (5.33 × 10^?9?1.97 × 10^?8 A/cm² under 100 kV/cm) smaller than those of pure BCZT films (1.02 × 10^?7 A/cm²).     

Fast response and broadband self-powered photodetectors based on CZTS/SiNW core-shell heterojunctions for health monitoring

In this work, fast response and broadband self-powered photodetectors based on heterojunctions of vertical smooth silicon nanowires (SiNWs) were proposed, which were achieved through spin-coating p-CZTS on top of n-SiNWs adopting a simple two-step method. First, CZTS was uniformly and tightly attached to the sidewalls of SiNWs in the form of nanoparticles. The prepared CZTS/SiNWs core-shell heterojunctions exhibited typical rectification characteristics in dark and excellent light response characteristics in light illumination. Our device could perform self-driven detection under the UV-VIS-NIR light irradiation without an external energy supply. The responsivity and specific detectivity were estimated to be 14 mAW^-1 and 1.5 × 10¹¹ Jones, which can be improved to 0.35 AW^-1 and 1.2 × 10¹³ Jones at ?1.5 V bias. In addition, the present device also possesses distinct advantages of a large I_light/I_dark ratio exceeding 4.25 × 10⁴, fast response rate with rise/fall times of 1.4/14.2 μs, and outstanding environmental stability. Finally, a heart rate health monitoring application by CZTS/SiNWs detector was proposed. All these results may pave a way for the real application of the self-driven detector in the field of health monitoring in the future.     

Electroactive polythiophene/polystyrene bottlebrushes as morphology compatibilizers in photovoltaic systems

Poly(3‐thiophene ethanol) (P3ThEt)‐graft‐polystyrene (PSt) bottlebrushes were synthesized and applied in active layers of poly(3‐hexylthiophene) (P3HT):phenyl‐C71‐butyric acid methyl ester (PC71BM) solar cells as morphology compatibilizers. In the presence of 15 wt% of P3ThEt‐graft‐PSt bottlebrush compatibilizers, the P3HT crystallite dimensions (D₍₁₀₀₎ = 45.67 nm and D₍₀₂₀₎ = 30.12 nm) and R_mean (38.96 nm) of PCBM clusters were the largest and the layer spacings were all the smallest (d₍₁₀₀₎ = 1.054 nm, d₍₀₂₀₎ = 0.301 nm and d_(PCBM) = 0.406 nm). These dimensional properties led to better hole (1.9 × 10^?3 cm² V^?1 s^?1) and electron (1.2 × 10^?2 cm² V^?1 s^?1) mobilities. The content of bottlebrushes was optimized at 15 wt%, and thereby the best photovoltaic results including the maximum cell efficiency of 5.37% were obtained for this turning point (12.75 mA cm^?2, 61%, 0.69 V). On exceeding the optimum weight percentage, all photovoltaic parameters decreased markedly and reached even less than that of pristine devices (1.92% versus 2.24%). After an optimum weight percentage of compatibilizers, further enhancement in bottlebrush content in active layers saturated and finally oversaturated the system and, consequently, the cell parameters significantly decreased. Accumulation of bottlebrushes in interfaces and donor/acceptor phases ruined the system function even with large and packed P3HT crystallites and PC71BM clusters. © 2019 Society of Chemical Industry     

Depolarization electric field and poling voltage-modulated Pb,La(Zr,Ti)O3-based self-powered ultraviolet photodetectors

Traditional self-powered ultraviolet photodetectors, which are usually designed based on p-n junction interfacial effects, exhibit low responsivity and specific detectivity because the photogenerated electrons and holes cannot be separated effectively. Unlike wide band-gap semiconductor materials, ferroelectrics have large remnant polarization and thus high depolarization electric field throughout the whole bulk region, which can cause effective separation of photogenerated electrons and holes. Based on this, in this study, we prepare Pb_0.93La_0.07(Zr_1-xTi_x)_0.9825O₃ (PLZT) ferroelectric thin films with large remnant polarization and self-powered ultraviolet photodetectors with Au/PLZT/FTO structure. The results indicate that the photoelectric response performances of the detectors improve as the remnant polarization of the PLZT thin film and positive poling voltage increase. By adjusting the Ti content, due to large remnant polarization of 47.4 μC/cm² in the PLZT thin films with 80 mol% Ti, the corresponding photodetector exhibits the best self-powered ultraviolet photoelectric response with the high photo/dark current ratio of 2600, responsivity of 2.05 mA/W, specific detectivity of 5.45 × 10¹⁰ Jones, and fast response speed (rise time of 18 ms). These values are superior to those of recently reported self-powered ultraviolet photodetectors.     

Highly transparent Yb:Y2O3 ceramics obtained by solid-state reaction and combined sintering procedures

(Y_0.87-xLa_0.1Zr_0.03Yb_x)₂O₃ (x?=?0.02, 0.04, 0.05) transparent ceramics were obtained by solid-state reaction and combined sintering procedures with La₂O₃ and ZrO₂ as sintering additives. A method based on two-step intermediate sintering in air followed by vacuum sintering was applied in order to control the densification and grain growth of the samples during the final sintering process. The results indicate that La₂O₃ and ZrO₂ co-additives can improve the microstructure and optical properties of Yb:Y₂O₃ ceramics at relatively low sintering temperature. On the other hand, the addition of Zr⁴⁺ ions leads to the formation of dispersed scattering volumes in the ceramic bodies. Transmittance of 78.8% was measured for the 2.0?at% Yb:Y₂O₃ ceramic sample at the wavelength of 1100?nm. The spectroscopic properties of Yb:Y₂O₃ ceramics were investigated at room temperature. The obtained results show that the absorption cross-section at 978?nm is in the range of 2.08?×?10^–20 to 2.36?×?10^–20 cm², whereas the emission cross-section at 1032?nm is ~1.0?×?10^–20 cm².     

Thermal properties of Cf/HfC and Cf/HfC-SiC composites prepared by precursor infiltration and pyrolysis

Ultra-high temperature ceramic infiltrated carbon-fibre composites were prepared by precursor infiltration and pyrolysis (PIP) using a laboratory synthesized precursor. Microstructures and thermal properties including thermal expansion, thermal diffusivity, specific heat capacity and oxidative stability are correlated. XRD reveals the presence of C_f-HfC and C_f-HfC-SiC phases without formation of oxides. The CTE observed at 1200?°C is slightly higher for C_f-HfC (3.36?×?10^?6?K^?1) compared to C_f-HfC-SiC (2.95?×?10^?6?K^?1) composites. Lower thermal diffusivity of the C_f-HfC-SiC compared to C_f-HfC composites is attributed to a thermal barrier effect and cracks in the composites which formed due to the CTE mismatch between carbon fibre and the matrix as well as CO generated during graphitization. The thermal conductivity of C_f-HfC (4.18?±?0.14?Wm^?1?K^?1) is higher than that of C_f-HfC-SiC composite (3.33?±?0.42?Wm^?1?K^?1). Composites microstructures were coarse with some protruding particles (5?μm) with a homogeneous dense (～70%) matrix (HfC and HfC-SiC) for both composites.     

Microstructure,mechanical, tribological,and oxidizing properties of AlCrSiN/AlCrVN/AlCrNbN multilayer coatings with different modulated thicknesses

Multilayer structure design is one of the most promising methods for improving the comprehensive performance of AlCrN-based hard coatings applied to cutting tools. In this study, four types of AlCrSiN/AlCrVN/AlCrNbN multilayer coatings, with different modulated thicknesses, were deposited to investigate their microstructure, mechanical, tribological, and oxidizing properties. All multilayer coatings exhibited grain growth along the crystallographic plane of (200) with a NaCl-type face-centered cubic (FCC) structure. The results show that, as the modulation thickness decreases from ～35 nm to ～10 nm, (1) the grain refinement effect is increasingly evident; (2) all multilayer coatings show a hardness of >30 GPa and an elastic modulus of >300 GPa. Both the ability to resist elastic strain to failure and the plastic deformation of multilayer coatings increase. In addition, their resistance to cracking reduces; (3) the wear rates of these multilayer coatings reduce successively from 1.78 × 10^?16 m³ N^?1 m^?1 to 7.7 × 10^?17 m³ N^?1 m^?1. This is attributed to an increase in self-lubricating VO_x and a decrease in adhesives from the counterparts; (4) the best high-temperature oxidation resistance was obtained for the multilayer coating with a modulated thickness of ～15 nm.     

WSe2/2D electron gas heterojunction on KTaO3 for room-temperature giant photoconductivity

Van der Waals (vdW) heterojunctions, based on 2D systems, show great potential as high-performance photodetectors. Recent advances have reported an Ar⁺-ion-bombardment assistant method to achieve a vdW heterojunction between a 2D-material and a 2D electron gas (2DEG). Here, we fabricate a vdW heterojunction between WSe₂ and 2DEG on KTaO₃. Under visible light illumination, a giant photoconductivity is observed with bias voltage applied at room temperature. Such a device exhibits an instantaneous photoelectric response to on/off light illumination. The ratio of on/off currents reaches as high as 10⁴. In the wavelength range of 405–808 nm, the photoresponsivity is much greater for shorter wavelengths, reaching a maximum of 1.84 A/W. Moreover, even without bias voltage, the WSe₂/2DEG heterojunction still generates a short-circuit photocurrent due to the photovoltaic effect, implying a self-powered photodetector. This work paves a path towards high-performance photoelectric devices based on vdW heterojunctions of 2D-material/2DEG.     

Optical nonlinearity and photoinduced anisotropy of an azobenzene‐containing ionic liquid crystalline polymer

The nonlinear optical properties of an azobenzene‐containing ionic liquid crystalline polymer were investigated using single‐beam Z‐scan and optical Kerr effect (OKE). The polymer film exhibited large nonlinear absorption (～10^?6 cm W^?1) and nonlinear refraction (～10^?11 cm² W^?1) under 532 nm ps excitation. The femtosecond time‐resolved OKE results suggested that the nonlinear optical response time in off‐resonant region was as fast as 300 fs. Moreover, stable molecular reorientation and a large photoinduced birefringence ( ) were achieved in the polymer film with a 405 nm continous wave (CW) laser as pump light. The large optical nonlinearity, ultrafast response, and effective photoinduced molecular reorientation of the polymer films indicated their potential applications in nonlinear photonic devices and optical storage. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and characterization of polyaniline/NiO nanocomposite

Spherical nickel oxide (NiO) nanoparticles were prepared by using nickel chloride as precursor in the ethylene glycol as solvent and urea as precipitant. The X‐ray diffraction study showed that NiO has single‐phase cubic structure with average crystallite size of 35 nm. The prepared NiO nanoparticles were incorporated into polyaniline (PANI) matrix during in situ chemical oxidative polymerization of aniline with different molar ratios of aniline: NiO (12 : 1, 6 : 1, and 3 : 1) at 5°C using (NH₄)₂S₂O₈ as oxidant in aqueous solution of sodium dodecylbenzene sulfonic acid, as surfactant and dopant under N₂ atmosphere. The synthesized composites have been characterized by means of X‐ray diffraction (XRD), thermogravimetric analysis, Fourier transform infrared (FTIR), scanning electron microscopy, TEM, and vibrating sample magnetometer for its structural, thermal, morphological, and magnetic investigation. The XRD and FTIR studies show that the NiO particles are in the composite. The room temperature conductivities of the synthesized PANI, PANI/NiO (12 : 1), (6 : 1), and (3 : 1) composites were found to be 3.26 × 10^?4, 1.88 × 10^?4, 1.5 × 10^?4, and 4.61 × 10^?4 S/cm, respectively. The coercivity (H_c) and remnant magnetization (M_r) of NiO, PANI/NiO NCs (12 : 1), (6 : 1), and (3 : 1) at 5 K was found to be 8.22 × 10^?2, 6.31 × 10^?2, 6.42 × 10^?2, 6.27 × 10^?2 T, and 6.64 × 10^?3, 1.83 × 10^?4, 3.07 × 10^?4, and 3.98 × 10^?4 emu/g, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Yb/Er/Ho-α-SiAlON ceramics for high-temperature optical thermometry

Maximum operating temperature in optical thermometry is limited due to poor thermal stability of the sensing material at high temperatures. Here, Yb, Er and Ho-doped α-SiAlON (Yb/Er/Ho-α-SiAlON) ceramic prepared by hot press method has been studied for optical thermometry via upconversion under 980 nm excitation. The phase of the sintered ceramic has been confirmed by Rietveld refinement of the X-ray diffraction data. The temperature-dependent upconversion was studied in a wide temperature range of 298–1023 K and fluorescence intensity ratio technique was used for temperature sensing behavior. Excellent spectral/thermal stability over the investigated temperature range was observed for the Yb/Er/Ho-α-SiAlON as the sensing material. The maximum values of absolute and relative sensitivity based on the thermally coupled levels of Er³⁺ are 59.2 × 10^?4 K^?1 and 1.10 %.K^?1 at 298 K and that based on non-thermally coupled levels are 108 × 10^?4 K^?1 at 385 K and 0.345 %.K^?1 at 329 K, respectively.     

The suppression of dark current for achieving high-performance Ga2O3 nanorod array ultraviolet photodetector

Gallium oxide (Ga₂O₃) is a promising candidate for next-generation solar-blind photodetectors (PDs) because of its large bandgap of 4.9 eV. Its single-crystal nanorod structure improves its photoelectric performance, which promotes carrier transformation and separation. However, Ga₂O₃ nanorods fabricated by the hydrothermal method have many oxygen vacancies, which largely enhance the dark current and reduce the on/off ratio of PDs, restricting application of such devices. Therefore, in this paper, dual strategies are applied to reduce the dark current of a metal–semiconductor–metal-structured Ga₂O₃ nanorod PD fabricated by the hydrothermal method. Through these dual strategies, which include annealing treatment and the application of a polymethyl methacrylate (PMMA) coating, the dark current of the PD is reduced from 1.34 × 10^?7 to 2.04 × 10^?9 A at 1 V, resulting in the on/off ratio of the PD reaching as high as 3.24 × 10⁴. Besides, the responsivity and detectivity of the device reach 1.73 A/W and 2.53 × 10¹² Jones respectively, which represents better performance than those of other reported Ga₂O₃ nanorod array PDs. Results have shown that the new strategy adopted can greatly improve the performance of Ga₂O₃-based ultraviolet photodetectors.